In a landmark judgement upholding freedom of expression, the Supreme Court today struck down a provision in the cyber law which provides power to arrest a person for posting allegedly "offensive" content on websites.

Terming liberty of thought and expression as "cardinal", a bench of justices J Chelameswar and R F Nariman said, "The public's right to know is directly affected by section 66A of the Information Technology Act."

Justice Nariman, who pronounced the verdict in a packed court room, also said that the provision "clearly affects" the fundamental right to freedom of speech and expression enshrined under the Constitution.

Elaborating the grounds for holding the provision as "unconstitutional", it said terms like "annoying", "inconvenient" and "grossly offensive", used in the provision are vague as it is difficult for the law enforcement agency and the offender to know the ingredients of the offence.

The bench also referred to two judgements of separate UK courts which reached different conclusions as to whether the material in question was offensive or grossly offensive.

The government had also said that it will not misuse the provision.

"Governments come and go but section 66A will remain forever," the bench said, adding the present government cannot give an undertaking about its successor that they will not abuse the same.

The bench, however, did not strike down two other provisions- sections 69A and 79 of the IT Act- and said that they can remain enforced with certain restrictions.

Section 69A provides power to issue directions to block public access of any information through any computer resource and 79 provides for exemption from liability of intermediary in certain cases.

The apex court pronounced its verdict on a batch of petitions challenging constitutional validity of certain sections of the cyber law.

The first PIL on the issue was filed in 2012 by law student Shreya Singhal, who sought amendment in Section 66A of the Act, after two girls -- Shaheen Dhada and Rinu Shrinivasan -- were arrested in Palghar in Thane district as one of them posted a comment against the shutdown in Mumbai following Shiv Sena leader Bal Thackeray's death and the other 'liked' it.

In the wake of numerous complaints of harassment and arrests, the apex court had on May 16, 2013, come out with an advisory that a person, accused of posting objectionable comments on social networking sites, cannot be arrested without police getting permission from senior officers like IG or DCP.

After the apex court had reserved its judgement in the matter on February 26 this year, another controversial case hogged the limelight for alleged misuse of section 66A, in which a boy was arrested on March 18 for allegedly posting on Facebook objectionable comments against senior Samajwadi Party leader Azam Khan.

A petition was filed before the Supreme Court in this regard alleging that its advisory was violated after which the apex court had asked UP police to explain the circumstances leading to the arrest of the boy.